Hello,

I'm having difficulty in understanding where the book has got these angles from:

Question: Find the maximum and minimum values for

Now, in my book the answer is 5 at for a maximum value, and -5 at for a minimum value. However, they have subtracted from in order to obtain these pair of angles? I've drawn the function, and these values is where . As a matter of fact, the maximum value first occurs at and the minimum value at .

I've looked into this a bit deeper, and the only way a maximum or minimum value can occur at these computed angles - is if the first derivative is a negative cosine function.

What have I done wrong?

Thank you for your attention.